Evaluation of Soil Streptomyces spp. for the Biological Control of Fusarium Wilt Disease and Growth Promotion in Tomato and Banana

Abstract

Fusarium oxysporum f. sp. lycopersici (Fol) and Fusarium oxysporum f. sp. cubense (Foc), are the causal agent of Fusarium wilt disease of tomato and banana, respectively, and cause significant yield losses worldwide. A cost-effective measure, such as biological control agents, was used as an alternative method to control these pathogens. Therefore, in this study, six isolates of the Streptomyces-like colony were isolated from soils and their antagonistic activity against phytopathogenic fungi and plant growth-promoting (PGP) activity were assessed. The results showed that these isolates could inhibit the mycelial growth of Fol and Foc. Among them, isolate STRM304 showed the highest percentage of mycelial growth reduction and broad-spectrum antagonistic activity against all tested fungi. In the pot experiment study, the culture filtrate of isolates STRM103 and STRM104 significantly decreased disease severity and symptoms in Fol inoculated plants. Similarly, the culture filtrate of the STRM304 isolate significantly reduced the severity of the disease and symptoms of the disease in Foc inoculated plants. The PGP activity test presents PGP activities, such as indole acetic acid production, phosphate solubilization, starch hydrolysis, lignin hydrolysis, and cellulase activity. Interestingly, the application of the culture filtrate from all isolates increased the percentage of tomato seed germination and stimulated the growth of tomato plants and banana seedlings, increasing the elongation of the shoot and the root and shoot and root weight compared to the control treatment. Therefore, the isolate STRM103 and STRM104, and STRM304 could be used as biocontrol and PGP agents for tomato and banana, respectively, in sustainable agriculture.

Keywords: Fusarium wilt; Streptomyces; biocontrol; plant growth promoting.

Fig. 1

Phylogenetic relationship of the six strains of Streptomyces spp. based on partial 16S rDNA gene sequences. A neighbor-joining tree was constructed using Mega 6. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1,000 replicates) is shown next to the branches (cut-off value of 50%). Pictures shown on the right side are a colony and spore-chain morphology.

Fig. 2

Fusarium wilt disease symptom in tomato after 4 weeks of Fusarium oxysporum f. sp. lycopersici (Fol), isolate TFPK101 and TFPK401 inoculation. Culture filtrate of Streptomyces sp. isolate STRM103 and STRM104 were drenched on the soil near the tomato’s root crown 2 days before Fol inoculation and every week after Fol inoculation.

Fig. 3

Fusarium wilt disease symptom in banana after 4 weeks of Fusarium oxysporum f. sp. cubense (Foc) isolate KPS1-3 and PT4-3 inoculation. Culture filtrate of Streptomyces sp. isolate STRM304 was drenched on the soil near the banana’s root crown 2 days before Foc inoculation and every week after Foc inoculation.